1. Field of the Invention
The present invention relates to a disk player for reproducing or recording recording information from or onto a disk type information recording medium with high recording density which is represented by DVD. Such a disk type information recording medium is DVD-Rewritable (hereinafter, referred to as DVD-RW) onto which the recording information can be written and where prepits are previously formed as various control information such as address information.
2. Description of the Related Art
As mentioned above, in a disk type information recording medium such as DVD-RW, prepits are formed in advance on the disk as preformed information which indicates various control information such as address information When the recording information is recorded or reproduced, the prepits are detected so that necessary control information can be obtained.
In the DVD-RW, for example, an information pit is formed on a groove track by changing reflectance in accordance with a crystal state or non-crystal state, and a prepit is previously formed on a land track as an uneven phase pit.
In an optical pick-up which is generally used for reproducing/recording information from/onto the disk type information recording medium, 4-divided light receiving elements are frequently used in order to realize focusing servo by means of astigmatism and tracking servo by means of push-pull. The 4-divided light receiving elements are also used for the detection of the prepits.
For example as shown in FIG. 7, a reflected light of a beam spot emitted onto the groove track 1 is divided into four areas A through D by the light receiving elements so that respective detection signals are obtained, and a prepit 3 formed on the land track 2 is detected by obtaining (Axe2x88x92B)+(Dxe2x88x92C). The arrow in FIG. 7 shows the advance direction of the groove track 1. The advance direction of a light beam is opposite to the direction shown by the arrow in FIG. 7.
However, in the above-mentioned conventional prepit detection, a delay of the detection signals due to a property of the phase pit should be taken into consideration. Namely, in a disk type information recording medium such as DVD-R (DVD-Recordable), an information pit and a prepit are formed by making a substrate uneven so that a phase difference is given to the light beam, and the intensity of the light modulated by diffraction on the pit is detected. Therefore, because of a difference in properties such as diffraction efficiency and diffraction angle at the phase pits, detection timing varies in the respective areas of the light receiving elements.
FIG. 8 shows a conventional method of detecting the prepits using the conventional 4-divided light receiving elements. As is clear from FIG. 7, since the areas C and D of the four areas are in a forward position of a relatively forward direction of the light beam on the optical disk and the areas A and B are in a backward position, the detection timing of the information pit in the areas A and B is delayed from the detection timing in the areas C and D by xcex94t1. Meanwhile, as for the detection timing of the prepit, since a beam spot is on the groove track and the prepit is on the land track, diffraction property becomes complicated, and thus changes are made in the areas B and D earlier and changes in the areas A and C are delayed by xcex94t2. In addition, the changes in the areas A and D are made in a direction where the light intensity is weakened, and the changes in the areas B and C are made in a direction where the light intensity is strengthen.
When calculation is made according to Axe2x88x92B and Dxe2x88x92C, changed portions of the signals due to the information pit are canceled, and only changed portions due to the prepit remain. Finally, the prepit is detected by a signal calculated according to (Axe2x88x92B)+(Dxe2x88x92C). At this time, ml in the drawing is a prepit detecting range and is to be a detection margin. A threshold is set suitably within the range of ml so that the prepit is read.
At this time, in the case where the delay time xcex94t2 is zero, the prepit detecting range ml to be obtained must be larger. However, actually peaks of the changed portions due to the prepit do not coincide with each other because of the delay time xcex94t2, and thus ml becomes smaller. As a result, prepit detecting accuracy is restricted and an influence of malfunction due to a noise becomes great accordingly.
In addition, since the delay time xcex94t2 fluctuates depending on a cutting condition or the like of the prepit on the optical disk, it is not easy to predict an amount of the delay xcex94t2.
It is an object of the present invention to provide a disk player which is capable of obtaining prepit detection delay with high accuracy due to different areas of light receiving elements and to provide a disk player which is capable of preventing lowering of a detection margin of a prepit due to the detection delay and of detecting the prepit accurately without being influenced by a noise.
A disk player in accordance with the present invention is an apparatus for recording or reproducing recording information to a recording disk by emitting a light beam onto the recording disk. The recording disk has a recording track for recording the recording information, a guide track for guiding the light beam to the. recording track, and a prepit which is pre-formed on the guiding track and which serves as control information for controlling a recording operation or a reproduction operation of the disk player. The disk player includes a light receiving device that receives the light beam reflected by the recording disk and that has a light receiving surface in which a first receiving area, a second receiving area, a third receiving area and a forth receiving area are formed. The first receiving area and the second receiving area are located in a back area of the light receiving surface with respect to an advance direction of a relative movement of the light beam with respect to the recording track. The third receiving area and the fourth receiving area are located in a front area of the light receiving surface with respect to the advance direction of the movement of the light beam. The first receiving area and the fourth receiving area are located near the guide track on which the prepit is formed, as compared with locations of the second receiving area and the third receiving area. The disk player further includes a first generating device that generates a first difference signal indicating a difference between a first detection signal generated by the light beam that is received in the first receiving area and a third detection signal generated by the light beam that is received in the third receiving area; a second generating device that generates a second difference signal indicating a difference between a second detection signal generated by the light beam that is received in the second receiving area and a fourth detection signal generated by the light beam that is received in the fourth receiving area; and a phase difference detection device that detects a phase difference between the first difference signal and the second difference signal.
In the disk player in accordance with the present invention, when the recording track on the recording disk is irradiated with the light beam, the reflected light beam is received by the light receiving device having four receiving areas. Namely, the reflected light beam is received by the first receiving area, the second receiving area, the third receiving area and the fourth receiving area. Since the locations of the respective four receiving areas are different, the light beam is received in such a way that the light beam is divided into four parts.
When the light beam passes on the prepit, the change in the light beam occurs. This change is received by the respective four receiving areas. Because the locations of the respective receiving areas are different from each other, the timing and the direction of the change of the light beam caused by the prepit is different among the four receiving area.
In response to the reception of the light beam, four detection signals, namely, the first through fourth detection signals are generated. The four detection signals correspond to the four receiving areas, respectively. The change of the light beam caused by the prepit appears as a level change of each detection signal. Because of the difference of the locations of the respective receiving areas, the timing and the direction of the level change is different among the four detection signal.
As to the timing of the level change, the first detection signal and the third detection signal coincide with each other, and the second detection signal and the fourth detection signal coincide with each other. As to the direction of the level change, the first detection signal and the third detection signal are opposite to each other, and the second detection signal and the fourth detection signal are opposite to each other.
In consideration of this, the first difference signal which indicates the difference between the first detection signal and the third detection signal and the second difference signal which indicates the difference between the second detection signal and the fourth detection signal are generated. Thus, the level change caused by the prepit in the first detection signal and the third detection signal more clearly appears in the first difference signal. The level change caused by the prepit in the second detection signal and the fourth detection signal more clearly appears in the second difference signal.
The timing of the level change caused by the prepit is still different between the first difference signal and the second difference signal. This difference appears the phase difference between the first difference signal and the second difference signal. Therefore, in the disk player in accordance with the present invention, the phase difference detection device detects this phase difference.
Based on the detected phase difference, for example, the time difference between the first difference signal and the second difference signal can be compensated for each of individual recording disks. Accordingly, even if the manufacturing conditions of individual recording disks are different, the accurate phase difference can be detected, and, for example, the accuracy of the compensation of the time difference between the first difference signal and the second difference signal can be improved.
In the disk player in accordance with the present invention, a compensating device and a prepit signal generating device may be added. The compensating device is a device for generating a compensation signal by delaying the second difference signal by a delay time determined on the basis of the phase difference. The prepit signal generating device is a device for generating a prepit signal by adding the first difference signal to the compensation signal.
Based on the phase difference detected by the phase difference detection device, the difference in the timings of the level changes caused by the prepit between the first difference signal and the second difference signal is compensated by delaying the second difference signal in such a way that the timings of the level changes in the both signals coincide with each other.
Then, the prepit signal is generated by adding the first difference signal and the delayed second difference signal (i.e., the compensation signal). Because the timings of the level changes caused by the prepit in the first difference signal and the delayed second difference signal coincide with each other, the level change of the first difference signal and the level change of the delayed second difference signal are effectively added. Therefore, the large level change corresponding to the change of the light beam caused by the prepit appears in the prepit signal. Accordingly, even if noise is contained in the prepit signal, it is easy to distinguish the level change corresponding to the change of the light beam caused by the prepit from the noise. Therefore, the accuracy of the prepit detection can be improved.
In the disk player in accordance with the present invention, the compensating device may include: a control voltage setting device that sets a control voltage proportional to the phase difference; and a voltage control delay device that delays the second difference signal by a delay time corresponding to the control voltage. In such a disk player, the phase difference is easily converted into the delay time. Therefore, the accurate prepit detection can be achieved by such a simple construction.
In the disk player in accordance with the present invention, the phase difference detection device may detect the phase difference, while a detection of a recording mark formed on the recording track is not carried out. While the detection of the recording mark is carried out, the reflected light beam is relatively weak, and thus, it is difficult to detect the phase difference. Because of this reason, the phase difference detection is carried out, while the detection of the recording mark is not carried out. Therefore, the performance of the detection of the phase difference can be improved.
In the disk player in accordance with the present invention, the division of the respective four receiving areas in the light receiving surface of the light receiving device may be determined as follows. The back area of the light receiving surface is divided into the first receiving area and the second receiving area by a first division line. The front area of the light receiving surface is divided into the third receiving area and the fourth receiving area by the first division line. The light receiving surface is divided into the back area and the front area by a second division line. The first division line is approximately parallel to the recording track. The second division line is perpendicular to the first division line. The intersection of the first division line and the second division line is located within the light receiving surface.
In the disk player in accordance with the present invention, a delay device that delays a first difference signal may be added. Moreover, DVD-RW (DVD-Rewritable) may be used as the recording disk.
The nature, utility, and further feature of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.